Integrated circuits (ICs) are manufactured and tested in wafer form before being diced from the wafer and mounted in packages, modules, or directly on a printed circuit board. Wafer level IC testing is a critical part of the IC manufacturing process that identifies ICs that do not function properly and provides feedback for improving product design and reducing manufacturing cost. Wafer level IC testing also prevents non-functioning ICs from going through the cost of packaging and in some applications can be used for stress testing or burn-in testing at high temperature to screen ICs to improve long term reliability.
Conventional wafer IC testing uses probe cards to provide an electrical path between a test system and the pads on integrated circuits while in wafer form. Probe cards generally have electrical contact points (probe tips) that match the size and density of the electrical pads on an integrated circuit and conductive patterns that provide fan-out of electrical signals from these high density probes to the lower density connectors on the much larger printed circuit boards that interface to the IC tester. The probe card is typically held in place on a wafer prober, which moves the wafer into position to make an electrical connection between the IC pads and the probe tips on the probe card. After the integrated circuit or an array of integrated circuits has been aligned by the prober and has been electrically tested, the prober steps the IC wafer to the next integrated circuit or array of integrated circuits so that the next set of tests can be performed. The prober generally uses automatic pattern recognition optics to align the IC pads on the wafer to the tips of the probes on the probe card. After the wafer is in alignment for a test, the prober very precisely raises the wafer to push the probe contact points against aluminum, solder or other metal pad materials on the integrated circuits. The probes are typically individual springs, so the higher that the wafer is raised in contact with the probes, the greater is the force of the probes on the IC pads. The prober must raise the wafer high enough to create sufficient force to break through any oxides on the integrated circuit's metal pads and make a reliable contact but not raise the wafer so high that probe tips slide off the pads or that the probe tip force causes damage to the circuits under or near the IC pads. The probe card must compensate for mechanical tolerances in the manufacturing of the IC wafer, the probe contact points, the probe card electrical interconnect (printed circuit boards, ceramic substrates, flex circuits), and the prober. The probe card must also be designed to compensate for any mechanical movement due to heating of the wafer from the power generated by integrated circuits or by the prober performing high temperature testing as a reliability screen. The flexing or bending of the probe card under the force applied by the prober during testing must be limited, otherwise the probe tips will not stay in electrical contact with the IC pads. The probe card must maintain low contact resistance, consistent probe force and alignment during its operating life. Some probe card's applications can require a contact life of over a million test cycles.
A probe card analyzer is a metrology tool to ensure the quality of probe cards. Probe card analyzers can be used by probe card suppliers to verify that the probe card design is correct and that the newly manufactured probe card meets all of its electrical and mechanical specifications. Each IC design has a unique probe card that must be verified. IC manufacturers that buy probe cards may also use a probe card analyzer to verify the incoming quality of newly purchased probe cards, as well as for validating the functionality of the probe cards during the useful life of the prove cards.
Probe card analyzers need to test the electrical and mechanical properties of probe cards as well as the electrical properties of the components (e.g., relays, capacitors, and resistors) mounted on the probe card. Analyzers must check the electrical connections for resistance and leakage to each probe. Mechanically, the analyzer must determine whether the probe tip alignment and planarity meet the placement accuracy needed to make contact to all of the electrical pads on the IC wafer to be tested.
Due to the high throughput nature of semiconductor manufacturing, probe cards make thousands of test contacts a day and can make millions of test contacts over their lifetime. Over time, the repeated wafer testing can cause the probe tips to become misaligned, damaged or to pick up debris. This can result in incorrect test results and increased manufacturing costs. Probe card analyzers can be used to confirm that the probe card remains within specification throughout the life of the probe card. If the probe card drifts out of specification, the probe card analyzer provides data on what needs to be repaired and verifies that the repair process returns the probe card to its original design specifications.
The semiconductor industry's growth has been driven by delivering smaller, more complex ICs, which requires the number of interconnect pads on each IC to increase while the size of each pad shrinks. Also, to reduce the cost of wafer testing IC manufacturers are testing a larger number of ICs at the same time. This higher parallelism improves the IC tester utilization and reduces the total wafer test time and thus reduces the overall cost of tests. A few years ago, high pin count probe cards had 1,500 to 3,000 pins. The industry has introduced probe cards that can contact all of the ICs on a 300 mm wafer. These types of single touchdown memory probe cards can have up to 60,000 pins. These high pin count probe cards can require 2-5 grams of force for each probe to make contact during testing. This means that the probe card can exert a force of up to 300 Kg on the prober causing both the prober and the probe card to deflect and change the position of where the probes contact the IC pads. Traditional analysis systems for integrated circuit probe cards evolved from testing needle probe cards where there was a requirement to stop IC testing when yields dropped to analyze and adjust the needle's position and then go back to IC testing. Today, most advanced probe cards do not allow individual probe adjustments. So, the earlier test/adjust/test capabilities are no longer applicable for these applications.
FIG. 1 is a drawing representing a conventional probe card analyzer 10. Analyzer 10 includes a mechanical handler 15 that provides x, y, and z movement and holds probe card 20 with probes 25 that extend down from the probe card. Handler 15 has a top stage 50 that holds the check plates for electrical measurements, force measurement tools and a camera for measuring the optical planarity of probe tips. The check plate is connected to the measurement electronics through connector 30. The probe card 20 is connected to measurement electronics 60 through a cable 40, which is typically 1 to 3 meters long. A computer 65 communicates with a handler control 17 that communicates and operates x, y, z handler 15 through a cable 16. Computer 65 also communicates with measuring electronics 60 and synchronizes movements of handler 15 with measurements by measurement electronics 60. U.S. Pat. No. 4,918,374, entitled “Method and Apparatus for Inspecting Integrated Circuit Probe Cards,” describes a known apparatus and method for testing probe cards. Even though these conventional probe card analyzers attempt to replicate the same tester force loading conditions as seen in an IC test manufacturing environment, the mechanical handlers (e.g., handler 15) used for probe card analyzers generally do not deflect the same as the production wafer probers. U.S. Pat. No. 7,170,307, entitled “System and Method of Mitigating Effects of Component Deflection in Probe Card Analyzer,” describes an example of how probe card analyzers are attempting to increase their accuracy by placing a load on the probe card to minimize the effects of deflection while making probe card measurements.